1. Field of the Invention
This invention relates generally to the field of rigid disc drive data storage devices, and more particularly to an improved structure and mounting scheme for the voice coil motor used in the actuator that moves the read/write heads from track to track on the surface of the disc.
2. Brief Description of the Prior Art
Disc drive data storage devices of the type called "Winchester" disc drives are well known in the industry. Demands for increased performance and capacity have lead in recent years to the almost exclusive use of a voice coil motor (VCM) as the motive force to move the heads from track to track on the disc surface, and pressures for smaller form factors for the entire drive have again lead to almost total dominance in the marketplace of so-called "rotary VCM" actuators. In such an actuator, the read/write heads--and any associated dedicated servo heads--are cantilevered outward over the disc surfaces from a common pivot structure, while the coil of the VCM extends horizontally outward from the other side of the pivot structure. A permanent magnet and pole piece structure is fixedly mounted to the housing of the disc drive in such an arrangement that the flat coil is supported in the middle of the magnetic field formed by the permanent magnets. Sophisticated control logic applies a carefully calculated amount and polarity of DC power to the ends of the coil to controllably move the coil within the magnetic field, thus moving the heads, which are fixed in relationship to the coil, across the disc surfaces.
The current trend toward smaller form factors for disc drives has lead to the current generation of 3 inch and 2 inch disc drives, with smaller sizes yet in the planning and design stages. These small sizes have caused a significant reduction in the amount of space available for the mechanical components of the disc drive.
A typical voice coil motor (VCM) for imparting motion to the heads has commonly been built as a separate sub-unit of the disc drive and then installed inside a housing which controls contaminants in the area of the heads and discs. Such a motor usually consists of a vertical stack of components including a lower pole piece, a permanent magnet, a coil, and an upper pole piece, with an air gap on either side of the coil. Fastening this structure to a housing base and sealing the unit with a top cover creates a vertical accumulation of components and necessary air gaps that severely limits the amount of size reduction possible. Similarly, stacking all these components on top of one another causes a significant buildup of unavoidable tolerancing errors.
It is therefore desirable to create a disc drive incorporating a VCM which has a minimum vertical dimension and minimum areas for tolerance error buildup.